The space traveller tells the taxi driver: "I'm tired, hot and thirsty. Please drive me to a planet with water." The taxi driver quickly makes a selection from a cosmic armoury of possible routes. And where else to satisfy his fare's need for a long, cool drink and a nice, hot bath but good old, rain-soaked Earth?
Of course, when the girl who wants her pig to be at its heaviest possible weight in order to win a competition turns up, then the choice is heavy-gravity Jupiter. And what better than Pluto and its moon for the twins in search of a pair of two small planets?
Children can join these travellers on their fantastic journeys when they visit the Multimedia Gallery at the Royal Observatory in Edinburgh and log on to InterPlanetary Taxi - one of 10 space CD-Rom programs now available in the gallery at any one time.
Another program likely to appeal to the younger ones is Earth and Universe. It offers crisp images and simple, explanatory text on topics such as the solar system, gravity, stars and galaxies - followed by a test-yourself quiz.
The gallery, which opened last year, is part of the Observatory's Visitor Centre and of the move among exhibition centres in general to include as many interactive facilities as possible. It also signals that the academic astronomy community is waking up to the fact that it is not just scientists who crowd around telescopes whenever there is a chance to see phenomena such as shooting stars or a passing comet. Given the chance, the general public is in there, too.
For adults and the older school pupil the gallery has much to offer. Red Shift 2, for example, has 15 two-minute animations which illustrate, among other things, the birth of a star. A photo-gallery also offers 700 still images, along with accompanying text.
On its most sophisticated level the program acts as a global telescope. By keying in the appropriate latitude and longitude, you can select any piece of the Earth's sky for close examination. You can also generate 5,000 years' worth of time by creating your own animation of the sky's evolution.
But is there any insight into how the universe began in the first place? A few sections do dwell on the Big Bang, but a search for an answer to the question of when space or time began will be fruitless. But you can have a shot at playing God with a Dorling Kindersley package that allows you to select from a menu of elements to make your own planet.
Visitor Centre manager Des Baker casts aside notions of the gallery being used simply like a library. "It's lively rather than library," he says. Multimedia loudspeakers will certainly break the hallowed silence of academic settings, as will the buzz of visitors who are encouraged to move freely between one computer to the next.
The centre caters for around 20,000 visitors a year. It is anticipated that this figure will more than double should a bid to the Heritage Lottery Fund be successful; its facilities will be expanded into what is likely to be one of the most important space and astronomy centres open to the public in Europe. A successful bid will mean the most up-to-date computers and a definitive range of CD-Rom astronomy programs.
The gallery is halfway there: it is wired to the Internet via a demonstration machine and through the Observatory's Website. Its scope is now - if not cosmic - at least worldwide.
* Royal Observatory, Blackford Hill, Edinburgh EH9. Tel: 0131 668 8100. http:www.roe.ac.uk